By way of background, in marking systems such as xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor belt or drum surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the belt or drum photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner being electrostatically attached to the latent electrostatic image areas creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material such as paper and the toner image is fixed thereto to form a permanent record corresponding to the original.
In these electrostatic marking systems, a photoreceptor belt or drum surface is generally arranged to move in an endless path through the various processing stations of the xerographic process sequentially such as a charging station, an exposure station, a development station, a transfer station, a detack station, a fusing station and a cleaning station. Sometimes, as noted, the photoreceptor or photoreceptor surface is in the form of an endless belt and in other systems it is in the form of a drum. In this endless path, several xerographic-related stations are traversed by the photoconductive belt or drum and become worn. Each of these belts is exposed to friction and moved by rollers that provide the belt movement to accomplish the belt purpose. Since the photoreceptor surface is reusable when the toner image is transferred to a final support material such as paper, the surface of the photoreceptor (PR) is constantly abraded and cleaned by a blade and/or brushes and prepared to be used once again in the marking process. The transfer process from the PR to paper uses mechanical devices such as transfer assist blades which can have adverse effects on the final image.
Transfer Assist Blades (TAB's) are devices which apply pressure to the back side of a sheet of media in the transfer zone of a xerographic printing machine. The pressure holds the media against the photoreceptor to improve the transfer of toner to the media. Transfer assist blades are mechanical devices that wear and require replacement. These mechanical devices are moved in and out of a functional position as each sheet of paper enters and exits the transfer zone. If the device is in the functional position between sheets of media, the blade can become contaminated with toner from the inner document patches used for xerographic setups. This contamination can then be transferred to the back side of future media sheets and this is an undesirable condition.
The function of the transfer assist blade is to apply a pressure to the back side of a media forcing it against the imaged photoreceptor. This pressure is applied by pulling the TAB blade petals down against the lifters fingers associated with the separate petals thus forcing of the tips of the transfer assist blade petals against the media. The lifter fingers act as fulcrums as in a see-saw. As the one side of the petal gets pulled down by the TAB extrusion (the part that the petals are mounted onto), the other side rises up against the media. The transfer assist blade is comprised of many independent segments called petals. The lifter fingers are comprised of an outboard solid (non-moving) finger (which is the width of the smallest width sheet the machine will run) and independent fingers that can be raised to act as a fulcrum under the matching petals of the TAB blade when wider media is used. The independent lifter fingers are activated based upon the width of the media currently being printed. If the media is narrower than the full process width, the inboard lifter fingers are not engaged as media enters the transfer zone. If they were activated, the blade petals would contact the photoreceptor not covered by paper or media causing scratches on the photoreceptor surface. These scratches would first cause potential defects in the customer prints once a full width media was being printed again. Secondly, the life of the photoreceptor would be reduced because of these scratches which would drive up printing costs.
TAB Blade petal pressure against the paper can vary for a variety of reasons including the nature of the petals acting at the unmoving and the adjacent moving finger, the distance the petals have to travel “transfer gap”, the type of paper media being used, the condition (wear) of the TAB Blade, TAB home position setup and so on. These subtleties of differing pressure against the width of the paper may produce various image artifacts and defects along the width and length of the document.
Currently, the method to assess differing pressure uniformity across the paper width can only be done manually in an open loop mode by trained service personnel. Using trained service personnel involves a financial cost and lost time to the service organization and customer. The current approach is a one time setup. If a problem resurfaces, the lengthy service cycle begins all over again. A problem may not be known until a customer starts a job, or worse, it could occur during a job.